1. Field of the Invention
The present invention relates to a water injection Diesel engine.
2. Description of the Prior Art
As means for effectively reducing nitrogen oxides (NO.sub.x) in the exhaust gas of a Diesel engine and reducing the exhaust black smoke and fuel consumption rate of the engine at the same time, there exists a conventional Diesel engine of the type capable of injecting fuel and water from a common fuel injection valve, as shown in FIGS. 10 and 12.
In these Figures, reference numeral 1 designates a fuel tank, numeral 2 a fuel feed pump, numeral 3 a fuel injection pump body, numeral 4 a fuel injection plunger, numeral 5 a plunger barrel, numeral 6 a discharge valve, numeral 7 a check regulator valve disposed in a side passage of the discharge valve 6, numeral 8 a fuel injection tube (fuel feed passage), numeral 40 a fuel/water injection valve, numeral 9 the body of the injection valve 40, numeral 10 an injection port, numeral 11 a valve needle, numeral 12 a fuel reservoir, and numeral 14 a spring for biasing the needle valve 11.
On the other hand, numeral 19 designates a water tank, numeral 18 a water feed pump, numeral 17 a water feed tube, numeral 16 a water feed control valve, numeral 15 a water feed tube, and numeral 13 a water feed check valve for checking the backward flow of water to the control valve. Moreover, numeral 20 designates a control unit for controlling the amount of water to be fed and the feed timing. The control unit responds to a crank angle signal or other operating conditions of the engine to output a control signal to the control valve 16 via a line 23.
The body 9 of the fuel/water injection valve 40 is formed with a fuel passage 22 for establishing communication between the fuel injection tube 8 and the fuel/water injection valve fuel reservoir 12. On the other hand, the water feed check valve 13 communicates with a confluence 31 in the midst of the upper fuel passage 22 through a water passage 30 which is also formed in the body of the fuel/water injection valve 40.
Next, the operation of this system will be described.
The water pumped out of the water tank 19 by the water feed pump 18 is fed via the feed tube 17 to the control valve 16. For a quiescent period in which the plunger of the fuel injection pump 3 does not pump out the fuel, the control valve 16 is held in a open state for a predetermined period through the control unit to feed a predetermined amount of water to the fuel/water injection valve 40 via the feed tube 15. At this time, if the pressure at which the check regulator valve 7 of the fuel injection pump 3 opens is designated at P.sub.R whereas the pressure at which the water feed check valve 13 opens is designated at P.sub.P, the following relations hold for the pressure P.sub.O at which the valve needle 11 opens: EQU P.sub.O &gt;P.sub.R ; and P.sub.O &gt;P.sub.P.
Thus, the water fed flows into the fuel passage 22 via the check valve 13, the water passage 30 and the confluence 31.
The fuel residing in the fuel passage 22 upstream of the confluence 31, i.e., at the side of the fuel injection pump 3, is forced back toward the fuel injection pump 3 via the injection tube 8 by the fed water pressure so that it opens the check regulator valve 7 and flows into the plunger chamber.
As a result, as shown, the fuel/water injection valve 40 is filled with the fuel up to the capacity of V.sub.1 and V.sub.2, i.e., the sum of the capacity V.sub.2 of the fuel reservoir 12 and the capacity V.sub.1 of the fuel passage 22 from the confluence 31 to the fuel reservoir 12. The fuel passage 22 upstream of the confluence 31 is filled with a predetermined amount of water and further upstream with the fuel as shown in FIG. 11.
When the plunger 4 of the fuel injection pump 3 rises to start compressing the fuel, the pressure in the injection tube 8, the fuel passage 22 and the fuel reservoir 12 rises, and when it becomes equal to or exceeds the opening pressure P.sub.O of the needle valve 11 the needle valve 11 is opened. At this time, the water in the water passage 30 is not returned to the water tank 19 owing to the check valve 13.
When the valve needle 11 reaches its opening pressure P.sub.O, the injection port 10 of the fuel/water injection valve 40 of FIG. 12 injects: the fuel in an amount of V.sub.1 +V.sub.2, which has filled the fuel reservoir 12 and the fuel passage 22 up to the confluence, then the water of the predetermined fed amount, and finally the remaining fuel. If the amount of fuel to be injected by a single action is designated as Q.sub.F, the amount Q.sub.FP of fuel to be injected at first is expressed by Q.sub.FP =V.sub.1 +V.sub.2, as has been described hereinbefore. The total amount Q.sub.W of water is then injected, and the remaining amount of fuel Q.sub.FS is finally injected in an amount as expressed by Q.sub.FS =Q.sub.F -Q.sub.FP.
As a result, the ignition at an initial stage of the fuel stroke of the Diesel engine is ensured with the fuel in the amount Q.sub.FP. Subsequently, the suction of air into the sprayed atmosphere is increased by the water in the amount Q.sub.W so that the burning rate is raised to reduce the production of black smoke. At the same time, the water is introduced into the flame zone to reduce the NO.sub.x.
According to the prior art, the reducing effect of NO.sub.x in the exhaust gas is substantially proportional to the amount Q.sub.W of injected water. If, however, the water amount Q.sub.W is excessively increased relative to the fuel amount Q.sub.F, the time interval between the primary and secondary fuel injection amounts Q.sub.FP and Q.sub.FS is so elongated that the combustion becomes so insufficient that a stable engine operation cannot be achieved. In order to further reduce the NO.sub.x, therefore, there is required means for increasing the fuel injection amount Q.sub.W without any deficiency in combustion occurring.